Process for the manufacture of a resistant pulp for paper making



lMarch 3l, 1931. J. D. RUE 1,798,987

PROCESS FOR THE MANUFACTURE OF' A RESISTANT PULP FOR PAPER MAKING Filed sept] 1, 1928 Conce/1 fra/ed f'ra//y B/eaced I i. --J

Y Evaporaed Patented Mar. 31, 1931 UNITED STATES PATENT OFFICE JOHN D. RUE, F ASHEVILLE, NORTH CAROLINA, ASSIGNOR ro THE CHAMPION FIBRE COMPANY, 0F CANTON, NORTH CAROLINA, A CORPORATION 0F OHIO :PROCESS FOR THE MANUFACTURE OF A RESISTANT PULP FOR PAPER MAKING' Application filed September 1, 1928. Serial No. 303,573.

This invention relates to processes for the manufacture of chemical Wood pulp, and more particularly is concerned with the preparation from unbleached and impure pulp produced by the sulfate, or other chemical process, of a paper-making pulp characterized by a high degree of whiteness, of toughness, of strength, of resistance to mechanical treatment, and having an alpha cellulose content of from 88% to 94%. The invention also is concerned with such a process for the preparation of purified alkaline pulp interrelated with a simultaneous process for the production of unbleached and impure alkaline pulp upon which the purification procedure may be practiced.

In my copending application Serial No. 800,961, filed August 20, 1928, now Patent No. 1,771,064, issued July 22, 1980, there has been described and claimed a purification procedure for the preparation, from unbleached and impure alkaline pulp, of a purified pulp especially adapted for use in making paper, which purified pulp is characterized by a high degree of whiteness, strength, toughness, and resistance to mechanical treatment and having an alpha cellulose content of from 88% to 94%. The said procedure comprises the 'following sequence of operations:

(1) Partially bleaching an alkaline (i. e., sulfate, or soda) pulp, under such conditions as to represent what I term a drastic bleaching treatment, and washing the partially bleached pulp.

(2) Subjecting the partially bleached and washed pulp, suitably thickened, to treatment, at a temperature of from about 7 0 to about 212 F., for a period of from 10 minutes to about 6 hours, with a solution of a caustic alkali (e. g., caustic soda) in such concentration and in such proportion with respect ,to the pulp suspension that the resulting mixture has an alkalinity equivalent to that of a solution of caustic soda of from to-12% strength, and a pulp concentration of from 5% to 10%.

(3) Separating caustic alkaline liquor from the treated pulp of said mixture, and washing the treated pulp.

(4) Finally bleaching the treated and washed pulp,-preferably, at a 3% to 4% consistence,-and Washing the nally bleached pulp, Without, or preferably with, an intermediate treatment of the pulp, prior to the final washing, with an acid or acidic reducing agent in amount sufiicient to adjust the acidity of the pulp mass to a pH valuevof from 2 to 4.

The practicing of the above procedure upon an unbleached andimpure alkaline pulp effects a desirable purification thereof, Whereby there is obtained a purified pulp having the hereinbefore described favorable properties and characteristics. However, the procedure necessitates the use of relatively very large quantities of caustic alkali with respect to the qualities of pulp so treated, and it is desirable, therefore, to provide a means for adequate and economic re-use of the caustic alkali. o

The invention is based upon my discovery of the fact that, when partially bleached alkaline e., sulfate, or soda) pulp is treated with excess caustic alkaline solution under the conditions above specified, the caustic alkali is not consumed to any appreciable extent but that its action is like unto that of a catalyst, aiding in the chemical process which results in the dissolution of those constituents of the pulp whose removal is essential to the production of a product of the designated characteristics. I have found that the caustic alkali content of the separated caustic alkaline liquor is still available for re-use,-substantially in its entirety,- in the treatment of further charges of partially bleached pulp, or for the digestion of Wood for the production of alkaline pulp, or both. l

In accordance with the present invention, pulphaving the said designated properties and characteristics is produced according to a process, as illustrated in the flow sheet of the accompanying drawing, which comprises, as is indicated on said iiow sheet: thickening partially bleached and washed chemical wood the thickened pulp as to yield a mixture having a pulp content of. from 5% to 10% and an alikalinity of suspending solution equiv alent to that of a solution of caustic soda of from 5% to 12% strength; digesting the mixture for a relatively short period of timee. g.,'from 10 minutes to about 6 hours, but preferably for about 1 hour-at a temperature of from to 212 F., preferably at about 125 F.; separating the caustic alkaline solution from the so-treated pulp; Washing the treated pulp and finally bleaching and Washing the same, either Without, or preferably with, prior addition of an acid or acidic reducing agent in quantity sufficient to adjust the acidity of the pulp to a pH value of from 2 to 4; fortifying a portion of the separated caustic alkaline solution either with solid caustic alkali or with a caustic alkaline solution of high density-e. g., 50% caustic soda liquor; using the so-fortified solution for the treatment of a further charge of partially bleached and washed chemical Wood pulp; concentrating-as, by evaporation,-the remaining portion of the separated caustic alkaline solution to a relatively high concentration; using one portion of the soconcentrated separated solution in the fortitication of the unconcentrated portion of the separated caustic alkaline solution; and using the remaining portion of the said concentrated portion of the separated solution as make-up liquor in the preparation of an alkaline cooking liquor for the alkaline digestion of Wood. Preferably, the process according to the invention is cyclic in its nature, the raw pulp product obtained from the alkaline digestion of Wood being partially bleached and Washed, and thereafter puried in the manner hereinbefore described. As Will be apparent, the alkali content ot' the Waste alkaline cooking liquor produced as a by-product in the alkaline digestion of Wood may be utilized for making up alkaline cooking liquor used in the said digestion operation, by concentrating, smelting and causticizing the said Waste alkaline cooking liquor in the known manner.

In the operation of separating the caustic alkali-treated pulp from the alkaline treating solution, substantially complete recovery of the said alkali can be eil'ected only in a solution Whose concentration has been reduced to some extent by wash water. If the Washing is carried out on the counter-current principle, minimum dilution of the separated alkaline treating solution is effected: however, only a portion of the volume of recovered alkaline solution can bel re-used directly in a subsequent alkaline treatment of partially bleached pulp, and that portion requires some fortification. While it is possible to concentrate the remaining portion to the desired degree for use in fortifying the unconcentrated portion, repeated re-use of the solution in its substantial entirety would in time result in an undesirable accumulation of the organic matter dissolved from the pulp during the alkaline treatment,

thus making it necessary to continuously or intermittently divert a part of the contaminated alkaline solution from the alkaline treatment cycle and to make up for the consequent loss of caustic alkali by additions of fresh caustic alkali, e. g., the concentrated caustic soda solution obtained from an electrolytic process of manufacture. I have found that this diverted part of the contaminated alkaline solution Astill is suitable for direct use in making up an alkaline cooking liquor for the digestion of Wood. The organic materials dissolved in the contaminated alkaline treating solution ap arently do not depreciate the value of the so ution as a cooking liquor.

With reference to the step of separating treated pulp from caustic alkaline /treating solution, the separation advantageously may be effected by means of difusers through which Wash liquid and the mixture to be separated are passed in counter current to each other.

The degree to which the evaporation of used alkaline treating solution is carried is determined by the economic quantity of alkali that can be brought into the process from external sources, and by the concentration desired of that portion of the solution which is subsequently used in the digesting of wood for pulp. A convenient concentration is approximately fifty (50%) per cent which is also the cencentration of alkalinsolution conveniently available fromran electrolytic caustic plant. While such a concentration is not essential to the use of the solution in the digesting of Wood for pulp, it is a desirable concentration for the reason that it serves to concentrate the digestion liquor, otherwise of low concentration, and thus facilitates the production of a digestion liquor of high degree of causticity.

The proportion of the concentrated alkaline treating solution that is diverted to the digestion of wood for pulp is determined by the degree to which it is necessary to reduce the content of organic matter in the said treating solution for subsequent alkaline treatments of pulp.

I claim: I

1. Process which comprises partially bleaching and washing an unbleached and impure chemical wood pulp, thickenin the partially bleached and Washed pulp, a 'xing therewith an alkaline treating solution and digesting the mixture, separating treated pulp from treating solution, concentrating a portion of the separated treating solution, combining the remainder of the separated treating solution with a portion of the so-concelitrated solution and re-using the resulting alkaline solution with additional caustic alkali as alkaline treating solution, and usin the remaining portion ofthe 'so-concentrate solution in an alkaline digestion of wood.

2. Process which comprises partially bleaching and Washing a raw alkaline wood pulp, thickening the partially bleached and Washed pulp, admixing therewith a caustic alkaline treating solution and digesting the mixture, separating the so-treated pulp from the caustic alkaline treating solution, concentrating a portion of the separated treating solution, combining the remainder of the separated treating solution with a part of the .so-concentrated solution and reusing the resulting alkaline solution with additional alkali as alkaline treating solution, using the remaining part of the concentrated solution as alkaline-cooking liquor in an alkaline digestion of wood, and using the resulting raw alkaline Wood pulp as starting material for a succeeding cycle of operations.

8. In a process of purifying alkaline Wood pulp involving the operation of digesting the pulp with an alkaline treating solution, the steps which consist in separating treated pulp from the alkaline treating solution, con-V centrating a portion of the separated treating solution, combining the remainder of the separated treating solution with a part ofthe so-concentrated solution and re-using the resulting alkaline solution with additional alkali as alkaline treating solution, using the remaining part of the concentrated solution as alkaline cooking liquor in an alkaline digestion of Wood, and using the resulting raw alkaline Wood pulp as starting material for a succeeding ,cycle-of operations.

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'liti ln testimony whereof, I ailix my signature.

JOHN D. RUE. 

